Torsional vibration is caused by periodic fluctuation generated by the torsion loads about its average value, commonly exists in devices of rotating machinery. Generally, the torsion and the vibration thereof have complex periodic characteristics which include the vibration from a series of frequency components such as cars, combustion engines on ships, drive systems of propeller shafts, and bump mechanisms, etc. If some frequency components of dynamic load tend to equal with the natural torsional frequency of a structure, the mechanism will be subjected from violent torsional resonances, which probably results in damage and failure of parts. Even a torsional vibration with small amplitude, which does not damage the equipment, it is still not allowed as it is harmful for the surrounding environment by the radiated vibration and noise.
Overall, the method to damp torsional vibration involves two kinds of matters: one is the method to deal with the device structure itself, the important aspect of which is to desynchronize the natural torsional frequency of a structure from the frequency of torsional load by designing vibration characteristics. Other is a function design, for instance, increasing number of cylinder for a combustion engine can even the torsional fluctuation and improve output power as well. However, increasing of the volume, weight will increase the manufacture cost and designing difficulties.
Other method is to design a special additional device to get a special function, typically such as the combination of flywheel and torsional vibration damper, and this kind of method has comparatively low cost and limited change for the main machinery.
Usually, the common torsional vibration dampers are passive and elastic damped, which utilize elastic element to isolate vibration in such a way that rubber or viscous fluid resists vibration and dissipates frictional heat transferred from kinetic and mechanical energy. In the principle of structure, flywheel is generally divided into two parts which are connected with each other by elastic element and may relatively move to an elastic range and between which high damping material is filled. The biggest disadvantage of the solution is that the damping apparatus with relative fixed system characteristics is apparently unable to meet the high requirements under the circumstances that the torsional frequency and amplitude endured rapidly change in a wide range. It is very important for modern rotating machines.
In addition to the passive mode structure as said above, the technology for semi-active one, the characteristic parameters of elastic element and damping element are vary real-time within a range when needed, is developed. However, the actual effect on torsional vibration reduction needs further observation.
Completely differing from two technology mentioned above, the present invention belongs to a method to eliminate vibration in active mode, which uses a control system to dynamically track multiple quantities of harmonics in torsional vibration, the frequency, the amplitude and the phase, to provide said electric torsional vibration damper with drive current, impels it to produce the transient torsion, equal in frequency, opposite in phase, corresponding in amplitude, then the effect of eliminating torsional vibration is achieved. The method takes the advantage of advanced technology of modern integrated circuit and effective control theory, realizes a prominent effect of eliminating torsional vibration and substantially decreases the requirements to change the device itself for reducing vibration.